Database management systems require acquisition of snapshots at given points in time during data update. Snapshots are used, for example, for data retention (backup) or for referencing data content at arbitrary points in time. Techniques used in snapshot acquisition include, for example, mirroring and techniques for maintaining read consistency using logging or mapping.
With techniques using logging, operations on a database are recorded as log data (or journal data), and snapshots can be acquired by going back to the points in time of the log data (UNDO logging).
With techniques using mapping, table data in a database has a recordable structure, and new records are added in the case of either INSERT or UPDATE, for example. Multiple transactions including access to the same database can thereby reference not only current records in the database but also records at given points in time dating back from the present (MVCC).
Also, with mirroring, a (replica/duplicate) database with exactly the same content as the main (master) database is created. By thus duplicating the databases, and then isolating one of the databases at a given point in time and referencing the isolated database, a snapshot at that point in time can be acquired.    Non-Patent Document 1: Ch. 13 Oracle Architecture (Supplement), [online], [searched May 22, 2009], <http://www.shoeisha.com/mag/windev/pdf/870603/windev0603—144_SQLServer.pdf>
With the above UNDO logging, a memory area for log data is necessary. Also, the user needs to tune the size of the log data area with consideration for transaction volume. With MVCC, data area is consumed whenever the database is updated, even when referencing or snapshot acquisition is not performed. As a result, the data area is constricted. Also, unnecessary data area needs to be periodically recovered, with the CPU and I/O resources being used in recovery. With the above snapshot acquisition by isolating duplicated databases, a volume disk needs to be procured, configured and managed. In the case where snapshot acquisition is requisite for any of the above conventional schemes, complex processing is thus necessary, resulting in much waste in procurement and use of computer resources and operational management of users.